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Quick Question about prehung door measurements

Quick Question about prehung door measurements

Old 05-25-16, 10:48 AM
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Smile Quick Question about prehung door measurements

I am installing my first prehung door from a pre-existing build. The measurement for the rough opening is 26 and 5/8". The prehung door says the rough opening needs to be 26". If I place a 1X4 in to make the space smaller I get a measurement of 25 and 15/16". My question is does the rough opening need to be the EXACT spec the prehung door states or can it be bigger or smaller and which way is better? bigger? or just a fraction smaller? Thanks in advance!!

Old 05-25-16, 11:35 AM
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It is a rough opening. Rough means about. It can be slightly larger or slightly smaller. Larger is generally easier to fill and make the door truly plumb.
Old 05-25-16, 01:00 PM
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Shims are used to plumb the door. Slightly larger just more shims. They sell door shims but I like #3 wood shakes*. They are wide and easy to use. Be sure the floor is level. If not you will have to shim if it has an attached threshold. If no threshold you can cut off the jamb on yhe high side.

*Go to real lumber yard not a home store for the shakes. They may have a damaged bundle they will sell. The one I shop at actually sells small bundles as door shims. Home stores may only have #1 but why over pay for shims.
Old 05-25-16, 04:10 PM
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Your 25 15/16" rough opening should work, but we don't know how plumb the opening is. Your door frame will probably be about 25 3/8"... so as long as your rough opening isn't more than 1/4" out of plumb, you will have enough room to install and plumb your new door using shims between the door jamb and the framing.

You will also want to level the head, so you usually want to begin by checking to see if the floor is level. If one end is high by 1/4", for example, it works well to know that in advance so that you can cut 1/4" off the door jamb on that side.

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